How does this medication work? What will it do for me?

Mefenamic acid belongs to the class of medications called nonsteroidal anti-inflammatories (NSAIDs). It is used to relieve moderately severe pain, such as muscular aches and pains, menstrual cramps, headaches, and dental pain.

Mefenamic acid relieves pain and inflammation as long as it is being taken, however it does not correct the cause of the pain.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

How should I use this medication?

The recommended adult dose (for people more than 14 years old) is 500 mg for the first dose followed by 250 mg every six hours as needed, usually not to exceed one week of treatment. In the case of menstrual cramps, treatment is usually not necessary for longer than two or three days.

Mefenamic acid is best taken with or after food.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones given here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not dispose of medications in wastewater (e.g. down the sink or in the toilet) or in household garbage. Ask your pharmacist how to dispose of medications that are no longer needed or have expired.

signs of meningitis not caused by infection (e.g., headache [severe], throbbing, or with stiff neck or back)

signs of a serious allergic reaction, e.g.:

abdominal cramps

difficulty breathing

nausea and vomiting

swelling of the face and throat

signs of a severe skin reaction, e.g.:

a rash combined with fever or discomfort

a rash covering a large area of the body

a rash that spreads quickly

blistering

peeling

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.

Allergy: Some people who are allergic to other NSAIDs or ASA also experience allergic reactions to mefenamic acid. Before you take mefenamic acid, inform your doctor about any previous adverse reactions you have had to medications, especially NSAIDs. People who have experienced difficulty breathing after taking ASA or other NSAIDs should not take mefenamic acid.

Contact your doctor at once if you experience signs of an allergic reaction, such as skin rash, itching, difficulty breathing or swelling of the face and throat.

Anemia: This medication may cause anemia (low red blood cells). If you take this medication for a long period of time, your doctor will periodically monitor your red blood cell levels. If you experience symptoms of anemia (e.g., shortness of breath, fatigue, pallor, fast heartbeat), contact your doctor as soon as possible.

Asthma: People with asthma are at increased risk of severe and even fatal allergic reactions (anaphylaxis) when taking this medication. People with asthma or other breathing disorders should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Bleeding disorders: Mefenamic acid may increase bruising and bleeding from cuts may take longer to stop. People with bleeding disorders, a history of bleeding problems, or those who are taking medications to prevent clotting, should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Blood pressure: Mefenamic acid may cause an increase in blood pressure, even when there have been no blood pressure problems in the past. People with high blood pressure should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication and whether any special monitoring is needed. Report any ongoing increase in blood pressure to your doctor as soon as possible.

Diarrhea: If diarrhea occurs, the dosage should be reduced or the medication stopped temporarily. Certain people who develop diarrhea may be unable to tolerate the medication in the future as well.

Fluid retention: Mefenamic acid can cause fluid retention and may result in swelling or puffiness. In severe cases, this can make symptoms of congestive heart failure worse. People with congestive heart failure should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication and whether any special monitoring is needed.

Report any fluid retention, swelling or puffiness in the legs, feet or hands, or any difficulty breathing, to your doctor as soon as possible.

Heart problems: Mefenamic acid, like other NSAIDs, may increase the risk of serious heart problems such as heart attack, stroke, or blood clots. People who are at risk for heart disease, such as high blood pressure, high cholesterol, diabetes, or pre-existing heart disease, should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication and whether any special monitoring is needed.

Kidney function: Long term use of mefenamic acid may lead to a higher risk of reduced kidney function. This is most common for people who already have kidney disease, liver disease, or heart failure; for people who take diuretics (water pills); and seniors.

People with kidney disease or reduced kidney function should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: People with liver disease or reduced liver function should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Stomach problems: Stomach ulcers, perforation, and bleeding from the stomach have been known to occur during therapy with mefenamic acid. These complications can occur at any time, and are sometimes severe enough to require immediate medical attention. The risk of ulcers and bleeding increases when higher doses of NSAIDs are taken for longer periods of time. Mefenamic acid may prolong stomach bleeding caused by ASA. However, mefenamic acid itself appears to be less likely than ASA to cause stomach bleeding.

People who easily experience irritation of the stomach and intestines, have had a stomach ulcer in the past or have another inflammatory disease of the stomach such as ulcerative colitis or Crohn's disease, should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication and whether any special monitoring is needed.

Stop taking the medication and contact your doctor immediately if you experience symptoms or signs that suggest stomach ulcers or bleeding in the stomach (black, tarry stools). These reactions can occur at any time during treatment without warning.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

The use of mefenamic acid during the last 3 months of pregnancy may result in harm to the baby or longer labour for the mother. Mefenamic acid should not be used during this time.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking mefenamic acid, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: Mefenamic acid is not recommended for children under the age of 18 years. The safety and effectiveness of using this medication have not been established for children.

Seniors: Seniors appear to have a higher risk of side effects, such as bleeding and kidney problems. The lowest effective dosage should be used for the shortest period of time possible.

What other drugs could interact with this medication?

There may be an interaction between mefenamic acid and any of the following:

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

stop taking one of the medications,

change one of the medications to another,

change how you are taking one or both of the medications, or

leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.